The present invention relates to an improved valve train for an internal combustion engine, and more particularly, to a valve deactivator assembly for use therein.
Although the valve deactivator assembly of the present invention may be utilized to introduce some additional lash into the valve train, such that the valves open and close by an amount less than normal, the invention is especially suited for introducing into the valve train sufficient lash (also referred to hereinafter as "lost motion"), such that the valves no longer open and close at all, and the invention will be described in connection therewith.
Valve deactivators of the general type to which the invention relates are known, especially in connection with internal combustion engines having push rod type valve gear trains in which there is a rocker arm, with one end of the rocker arm engaging a push rod, and the other end engaging the engine poppet valve. Typically, a central portion of the rocker arm is fixed relative to the cylinder head (or other suitable structure) by a rocker shaft assembly, as is well known to those skilled in the art. In such an arrangement, the rocker shaft prevents any movement of the rocker arm except a pivotal movement, wherein the rocker arm engages in cyclical, pivotal movement, in response to the cyclical motion of the push rod, which results from the engagement of the push rod with the cam lobe of the rotating cam shaft.
In a rocker arm and rocker shaft type of valve gear train as described above, it is known to separate the rocker arm into two separate rocker arm portions, each of which is mounted for pivotal movement relative to the rocker shaft. U.S. Pat. Nos. 4,576,128; 5,592,907 and 5,613,469 all illustrate valve gear train of the type described, wherein the two rocker arm portions may be selectively latched or unlatched to achieve either normal engine valve opening and closing, or modified opening and closing, respectively. One of the types of modified valve operation known from the above-cited patents is a condition in which the lost motion introduced into the valve gear train is sufficient to effectively stop or "deactivate" the valves, i.e., the valves do not open and close at all when the rocker arm portions are unlatched.
Typically, the types of engine valve modification systems illustrated and described in the cited patents have their rocker arm latching mechanisms operate in response to hydraulic pressure. Although such systems may be generally satisfactory, in the sense of being able to achieve a modification in the opening and closing of the engine valves, the arrangements described have certain inherent disadvantages.
One disadvantage is that the hydraulic systems for operating the latching mechanisms, as shown in the cited patents, are such that the hydraulic system (e.g., having the rocker shaft define oil passages) must be designed into the engine when the engine is designed initially, in order for the engine design process to be cost effective, whereas it would be desirable to be able to add valve deactivator assemblies to an existing engine design.
Another disadvantage of the prior art systems relates to time of response. In modern internal combustion engines, utilizing fuel injection, it is especially desirable in a valve deactivation system to turn off the fuel injectors at the same time that the operation of the valves is stopped. However, the fuel injectors are electrically actuated, and can be turned off almost instantaneously, and therefore, it is desirable to be able to activate the valves and turn on the fuel injectors, or deactivate the valves and turn off the fuel injectors, within the ensuing, single revolution of the engine cam shaft. Such rapid control of the valve deactivator would be difficult with hydraulic control thereof, in view of the fact that hydraulic controls are affected by factors such as aeration of the engine oil, variations in oil viscosity with variations in temperature, and pressure variations as engine speed varies. Thus, and by way of example only, in developing the present invention, the goal for the valve deactivator system was a maximum time of about 25 milliseconds from "ON" to "OFF", or vice versa.